I'm looking for a 5 V (not adjustable), 50 mA low noise voltage regulator.

Article describing their low quiescent current: digikey.com/en/articles/selecting-the-right-ultra-low-quiescent-current-ldo-regulator

Also, how did you find it? Please share so I can better find replacement components in the future.

 

I searched, "LDO Voltage Regulator" in Google. Went on Mouser (second link). Refined search results based on the criteria.

Also applied, "in stock" + "active" + "normally stocked":
https://www.mouser.com/Semiconducto...scv7Zgjdhub?P=1z0wsmtZ1z0shyuZ1z0wa29Z1z0z7pt

Unfortunately, there are none with the SOT-223-4 package.

Further restricting to 0.5-15 uA quiescent current, and sorted by price: https://www.mouser.com/Semiconducto...Z1yf9yyfZ1y9kwq8Z1yczb6vZ1ycyxqd&Ns=Pricing|0

I'm confused why all the chips besides the LM2936 and siblings are less costly...

 

I searched, "LDO Voltage Regulator" in Google. Went on Mouser (second link). Refined search results based on the criteria.

Also applied, "in stock" + "active" + "normally stocked":
https://www.mouser.com/Semiconducto...scv7Zgjdhub?P=1z0wsmtZ1z0shyuZ1z0wa29Z1z0z7pt

Unfortunately, there are none with the SOT-223-4 package.

Further restricting to 0.5-15 uA quiescent current, and sorted by price: https://www.mouser.com/Semiconducto...Z1yf9yyfZ1y9kwq8Z1yczb6vZ1ycyxqd&Ns=Pricing|0

I'm confused why all the chips besides the LM2936 and siblings are less costly...

Semiconductor pricing is mostly a function of supply and demand. The more demand there is the greater the supply, the more the supply increases, the lower the marginal cost of producing more. This situation will persist for some time until the demand decreases and the supply becomes more limited and the price starts to increase as the product approaches the "End of Life". Using a "Bathtub Curve" similar to the ones used in reliability and failure analysis is an often used model for semiconductor pricing over the lifetime of a product. It may be somewhat outdated given that we seem to be nearing a "feature size" limit that invalidates Moore's Law.